Glass used in buildings and vehicles, protects us generally from the environment (rain, wind, noise, etc.), allowing more pleasant conditions inside. However, ordinary glass does not protect from solar radiation, since it only absorbs a part of the UV radiation, reflecting a total of about 7% and transmitting much of the solar spectrum. In particular, in the case of the construction industry, the tendency is to use glass having solar control characteristics. This requires improvements in the properties of the glass (by means of coatings) to reduce entry of infrared radiation improving user comfort and reducing energy consumption.
The value added to the glass or other products can be increased depending on the functional properties conferred by its surface or a coating deposited thereon. Many phenomena that give functional characteristics to a material occur on the surface or in a region close to it. It is therefore possible to coat economical substrates (glass) with functional materials in the form of thin layers. Thus, the obtained product has the functional property of the coating and the characteristics of the substrate, particularly those of glass.
Solar control refers to the capacity to change the amount of transmitted or reflected solar radiation, in the near ultraviolet spectral ranges (UV; 300-380 nm), visible (VIS; 380-780 nm) and infrared (IR; 780-2500 nm). Low transmittance is generally pursued in UV and IR ranges, while the VIS transmittance may be high (>70%) or low, depending on the application.
In addition to blocking infrared radiation, glass and coating must have other properties, such as: high transmittance in the visible range (>70%), high mechanical strength, chemical resistance and weather resistance, it should be able to undergo heat treatments (tempering, bending), it must show a neutral color without iridescence, low dispersion and be low cost. The set of required properties makes development of such coatings a complex technological problem having great difficulty.
There are many choices for obtaining solar control properties. This is reflected in a lot of scientific articles, patents and patent applications existing on this matter. For example, a scientific publication on coatings with solar control properties, is the work “Solar heat reflective glass by sol-gel nanostructured multilayer coatings” by Z. Nagamedianova et al, published in the journal Optical Materials in 2011, Volume No. 33, pages 1999-2005; it describes commercial clear glass coated by the sol-gel method with three layers of oxides, TiO2—SiO2—TiO2, which have the property to reflect the IRC. Transmittances are reported in the VIS>70%, high UV blocking (Tuv<35%) and high reflectivity (>60%) in the 800-950 nm interval.
With regards to patents, U.S. Pat. No. 5,242,560 “Heat treatable sputter-coated glass” held by Guardian Industries Corp. describes a glass coated by sputtering which can be heat treatable consisting of one layer of Ni alloyed with one or two layers of Sn oxide, and optionally one intermediate Al layer.
The US Patent Application Publication No. 2011/0236715 A1 is related to a “solar control coating layer with discontinuous metal” held by PPG Industries Ohio, Inc. In that application a coating is proposed deposited over at least a portion of a substrate, comprising a stack metallic layers alternating with a plurality of dielectric layers, wherein at least one of the metallic layers comprising discontinuous metallic regions.
In the British Patent (1971) No. 1241889 “Heat reflecting glass and method for manufacturing the same” owned by Asahi Glass Co., Ltd., a glass substrate which reflects heat and transmits visible light, which comprises a composite of a metal oxide layer (TiO2, Ta2O5, WO3, ZrO2, Nb2O5, ThO2, SnO2) having a higher index than glass, in which microscopic metallic Pd or Au particles are immersed, is claimed.
Furthermore, there are several methods of synthesis of coatings which include: sol-gel, pulsed laser deposition, vacuum evaporation, electron beam, cathode pulverization, plasma discharge and CVD. A known process for applying layers or thin film coatings on glass sheets involves depositing metals or compounds derived therefrom by ion bombardment (sputtering) in a controlled vacuum on the glass surface, the positive gas ions are accelerated towards the cathode, the high voltage between the cathode and anode causes the gas ions to strike plates with sufficient energy to release atomic particles adhering to the glass. Deposition may be higher or lower depending on the amount of gas used, power and speed of the process conveyor.
Considering the above technique, the present invention relates to a multilayer coating with solar control properties, which is deposited on glass, intended for architectural, automotive, monolithic or laminated use. The coating is composed of several layers of different semiconductor metal oxides for solar control whose visible light transmission varies from 5 to 60%, a solar transmission from 5 to 40% and less than 0.5 solar factor.
From the above, the present invention relates to a substrate (glass) coated with a stack of films or thin layers, which are superimposed on the substrate in a predetermined order, i.e., in a first embodiment comprising: a glass substrate; a dielectric material (Si3N4); a layer of infrared reflecting metal (Nb); a protective material alloy (Ni—Cr) for protecting the metal layer from oxidation; a layer of metal material (TiN) to improve the surface properties of the substrate, reinforcing the mechanical and chemical protection of the coating on the substrate; and a dielectric material (Si3N4). The thicknesses of the layers are selected so that the coating confers to glass the solar control properties described in the preceding paragraph.
In a second embodiment, the coating comprises: a dielectric material (Si3N4); a second material with dielectric properties (TiO2); a layer of infrared reflective metal (Nb); a layer of metal material (TiN) to improve the surface properties of the substrate, reinforcing the mechanical and chemical protection of the coating on the substrate; and a dielectric material (Si3N4).